One-Dry, Two-Cool Process: A Key Core Technology for Upgrading Compound Fertilizer Quality

I. Overall Process Link: Wet granules after granulation → First drying (removal of free moisture) → First-stage cooling (rapid cooling and shaping) → Second-stage cooling (precise temperature control and dehumidification) → Finished product screening → Packaging and storage. The entire process achieves the processing goals of "controllable moisture, stable temperature, and dense granules." II. Core Configuration and Functions of Each Stage (I) Primary Drying: Laying the Foundation for Quality Core Equipment: A Φ2.0×20-meter drum dryer (suitable for 15-20 tons per hour) is selected, employing hot air circulation heating. The heat source can be natural gas, biomass pellets, or steam. Key Parameters: Drying temperature is controlled at 80-100℃, material residence time is 15-20 minutes, reducing the moisture content of the granulated pellets from 25%-30% to below 12%, with a drying uniformity error ≤2%. Technical Highlights: The dryer features a built-in spiral lifting plate layout, ensuring thorough material rotation and uniform heating; equipped with temperature and humidity sensors for real-time data feedback, and an automatic adjustment of hot air temperature and drum speed via a PLC system to prevent localized over-drying or incomplete drying. (II) Primary Cooling: Rapid Shaping and Increased Strength Core Equipment: A Φ1.8×18-meter counter-current cooler is configured, precisely matched to the dryer's capacity, employing a room-temperature air counter-current heat exchange design. Key parameters: Rapidly cools dried granules from 60-80℃ to 35-40℃ in 12-15 minutes, increasing granule strength from 1.5MPa to over 2.5MPa, effectively preventing pulverization during transport. Technical highlights: The cooler features a built-in air guide device to enhance heat exchange efficiency between airflow and granules; the outlet is equipped with a pulse dust collector to collect dust generated during cooling, with a dust emission concentration ≤10mg/m³. (III) Secondary Cooling: Precise Humidity Control for Stable Quality Core equipment: A Φ1.5×15 meter co-current cooler (or fluidized bed cooler) is used as a supplementary optimization step to the primary cooling. Key parameters: Further reduces granule temperature to room temperature ±3℃, stabilizing moisture content at 8%-10%, while removing trace amounts of residual free moisture from the granule surface, improving moisture resistance. Technical Highlights: Utilizing a low-temperature, low-wind-velocity design to prevent granule surface cracking; the cooling airflow can be flexibly adjusted according to ambient humidity, adapting to different regional climates and ensuring the finished product is less prone to clumping even in high-humidity environments.

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